Nutrition in Plants and Animals

Autotrophic nutrition

Organisms that synthesis of an organic compound from an inorganic source of carbon

Chemoautotrophic

are organisms that obtain their energy from simple inorganic reactions. E.g. Thiobacillus that oxidise hydrogen sulphide to sulphur. To process this carbon source, the bacteria require energy. These play a crucial role in the nitrogen cycle by converting ammonia into nitrite and nitrate, which can be used by other organisms. Some chemoautotrophs can also perform photosynthesis in addition to chemosynthesis, allowing them to utilize both sunlight and inorganic compounds for energy production. Most bacteria are chemotrophic

Colourless sulfur bacteria

oxidize hydrogen sulfide by accepting an electron from the compound. The acceptance of an electron by an oxygen atom creates water and sulfur. The energy from this reaction is then used to reduce carbon dioxide to create carbohydrates

Iron bacteria

Oxidise iron compounds and use the energy gained from this reaction to drive the formation of carbohydrates

Nitrifying bacteria

Oxidize ammonia to nitrate. Plants can use the nitrate as a nutrient source

Photosynthesis

The absorption of light by pigments such as chlorophyll, which is found in chloroplasts

Phatoautotriphic

are organisms that obtain their energy from light and use it to synthesise organic materials from inorganic sources. These organisms are typically plants, algae, and some bacteria. They use photosynthesis to convert light energy into chemical energy in the form of glucose. The light energy is used to split water molecules, releasing oxygen as a byproduct. The energy from the light is then used to convert carbon dioxide into glucose, which is used as a source of energy for the organism.

Chemostynthesis

using the oxidation of inorganic molecules as a source of energy; photosynthesis: using light as a source of energy

Leaf Structure Overview

The internal structure of a dicotyledonous leaf can be broken down into the following layers from the upper surface to the lower surface: Upper Epidermis, Palisade Mesophyll, Spongy Mesophyll, Vascular Bundles, Lower Epidermis

Upper Epidermis

This is the outermost layer of cells on the upper side of the leaf. It consists of a single layer of tightly packed, transparent cells without chloroplasts (except in guard cells). The upper epidermis is often coated with a waxy cuticle that minimizes water loss.

Palisade Mesophyll

Located just beneath the upper epidermis, the palisade mesophyll is composed of one or more layers of elongated, cylindrical cells that are rich in chloroplasts. These cells are arranged closely together and are the main site of photosynthesis due to their high chloroplast content

Spongy Mesophyll

Beneath the palisade mesophyll lies the spongy mesophyll. This layer consists of loosely packed, irregularly shaped cells that also contain chloroplasts, although in lower quantities compared to the palisade mesophyll. The spongy mesophyll has large air spaces between cells, which facilitate the diffusion of gases (CO₂,O₂, and water vapor) throughout the leaf

Vascular Bundles

The veins consist of xylem and phloem tissues surrounded by a bundle sheath. The xylem transports water and minerals from the roots to the leaf, while the phloem distributes the sugars produced during photosynthesis to other parts of the plant

Lower Epidermis

The lower epidermis is similar to the upper epidermis but contains more stomata (pores) for gas exchange. Each stoma is surrounded by a pair of guard cells that regulate the opening and closing of the stomatal pore

Location of Palisade Tissue

The palisade mesophyll is located beneath the upper epidermis and above the spongy mesophyll. It forms the top layer of the mesophyll in the leaf.

Function of Palisade Tissue

It is photosynthesis. The cells are packed with chloroplasts, which capture light energy to convert carbon dioxide and water into glucose and oxygen. The elongated shape of palisade cells maximizes light absorption by providing a larger surface area for chloroplasts to capture sunlight.

Structure of the leaves that help in Photosynthesis

The palisade mesophyll contains numerous chloroplasts that efficiently absorb sunlight. The spongy mesophyll facilitates the diffusion of gases, allowing carbon dioxide to reach the photosynthetic cells and oxygen to exit.

Structure of the leaves that help in gas exchange

The stomata in the lower epidermis control the movement of gases in and out of the leaf. Guard cells regulate the opening and closing of stomata to balance gas exchange with water loss. The air spaces in the spongy mesophyll increase the surface area for gas diffusion.

Structure of the leaf that help water transport and conservation

The xylem delivers water to the leaf tissues, while the waxy cuticle on the epidermis reduces water loss. Guard cells around the stomata help regulate transpiration.

Chloroplasts

The organelles where photosynthesis takes place. It is made up of the chloroplasts envelope, stroma, grana and thylakoid membranes and lamellae

Chloroplast Envelope

The chloroplast is surrounded by a double membrane known as the chloroplast envelope. This envelope consists of an outer membrane and an inner membrane. Both membranes act as barriers, controlling the movement of substances in and out of the chloroplast.

Stroma

The stroma is the fluid-filled space enclosed by the inner membrane. It contains enzymes, DNA, ribosomes, and other molecules necessary for the synthesis of organic molecules during the Calvin cycle. The stroma also contains starch granules and lipid droplets.

Grana and Thylakoid Membranes

Grana are stacks of membrane-bound structures called  thylakoids. Each thylakoid is a flattened sac, and the thylakoids within a granum are interconnected. The thylakoid membranes contain chlorophyll and other photosynthetic pigments, as well as proteins essential for the light-dependent reactions of photosynthesis.

Lamellae

The thylakoid membranes of different grana are connected by structures called stromal lamellae, which help maintain the structure and facilitate the transfer of materials between grana.

Location of Chloroplast Pigments

The main photosynthetic pigments (chlorophyll a and chlorophyll b) and accessory pigments (such as carotenoids) are embedded in the thylakoid membranes. These pigments absorb light energy and convert it into chemical energy during photosynthesis

Role of Chloroplast Pigments

1.       Light Absorption- Chlorophyll a: The primary pigment that absorbs light in the blue-violet and red wavelengths. It plays a central role in converting light energy into chemical energy. Chlorophyll b: An accessory pigment that absorbs light in the blue and red-orange wavelengths, transferring the captured energy to chlorophyll a. Carotenoids: These pigments absorb light in the blue-green wavelengths and provide photoprotection by dissipating excess energy.

2.       Energy Transfer- The absorbed light energy excites electrons in the chlorophyll molecules, initiating the light-dependent reactions of photosynthesis. These reactions generate ATP and NADPH, which are used in the Calvin cycle to produce glucose from carbon dioxide.

Absorption spectra

It is a graph of the relative amounts of light absorbed at different wavelengths by a pigment

Action spectra

It is a graph showing the effectiveness of different wavelengths of light in stimulating the process being investigated

Light Dependent reaction

The light-dependent reactions of photosynthesis occur in the thylakoid membranes of the chloroplasts. These reactions harness energy from sunlight to produce ATP and NADPH (reduced NADP⁺) and release oxygen as a byproduct. The light-dependent reactions can be categorized into cyclic photophosphorylation and non-cyclic photophosphorylation

Overview of Light dependent reactions

Purpose: To convert solar energy into chemical energy in the form of ATP and NADPH.
Location: Thylakoid membranes of the chloroplasts.
Key Processes:

• Absorption of light by chlorophyll

• Electron excitation and transfer through an electron transport chain (ETC).

• Production of ATP through chemiosmosis.

• Generation of NADPH by the reduction of NADP⁺.

• Evolution of oxygen from the photolysis (splitting) of water.

Non-Cyclic Photophosphorylation

Non-cyclic photophosphorylation is the primary pathway of the light-dependent reactions, involving both photosystem II (PSII) and photosystem I (PSI). This process results in the production of ATP, NADPH, and oxygen

Step by step process of non-cyclic photophosphorylation

1. Absorption of Light at Photosystem II (PSII): Light energy is absorbed by chlorophyll and other pigments in PSII, which boosts the energy of electrons (photoactivation). High-energy electrons are ejected from the reaction center (P680) of PSII and passed to the primary electron acceptor.

2. Photolysis of Water: The loss of electrons from PSII is compensated by splitting a molecule of water (photolysis) into oxygen, protons (H⁺), and electrons. The released electrons replenish those lost by PSII, and the oxygen gas is released as a byproduct. The reaction is: 2H₂O—>4H⁺ +4e^- +O₂

3. Electron Transport Chain (ETC): The excited electrons from PSII are transferred through a series of electron carriers in the thylakoid membrane, losing energy as they move along the chain. The energy lost by the electrons is used to pump protons (H⁺) from the stroma into the thylakoid lumen, creating a proton gradient (proton motive force).

4. Generation of ATP by Chemiosmosis: The buildup of protons in the thylakoid lumen creates a high concentration gradient relative to the stroma. Protons diffuse back into the stroma through ATP synthase, a protein complex embedded in the thylakoid membrane. The energy from the flow of protons drives ATP synthesis from ADP and inorganic phosphate (Pi). This process is called chemiosmosis.

5. Absorption of Light at Photosystem I (PSI): Electrons that have travelled through the ETC reach PSI, where they receive additional energy from light absorbed by the chlorophyll at the reaction center (P700). The re-excited electrons are transferred to another electron acceptor.

6. Formation of NADPH: The high-energy electrons from PSI are used to reduce NADP⁺ to form NADPH. The reaction is facilitated by the enzyme NADP⁺ reductase: NADP⁺ +2e^- + 2H⁺ —>NADPH+ H⁺. NADPH is then used as a reducing power in the Calvin cycle.

Products of non-cyclic photophosphorylation

·       ATP: Generated by chemiosmosis using the energy released during electron transport.

·       NADPH: Produced by the reduction of NADP⁺.

·       Oxygen: Released as a byproduct of water photolysis.

Cyclic Photophosphorylation

Cyclic photophosphorylation involves only photosystem I (PSI) and does not produce NADPH or oxygen. Instead, it generates additional ATP to meet the energy demands of the Calvin cycle

Step-by-Step process of cyclic photophosphorylation

1. Absorption of Light at Photosystem I (PSI): Light energy is absorbed by PSI, exciting electrons in the reaction center (P700). The excited electrons are passed to an electron acceptor and then travel through a series of electron carriers in the ETC.

2. Electron Transport and ATP Production: The electrons lose energy as they pass through the ETC, and this energy is used to pump protons (H⁺) into the thylakoid lumen, similar to non-cyclic photophosphorylation.  The proton gradient drives ATP synthesis via chemiosmosis.

3. Electron Recycling: Instead of being used to reduce NADP⁺, the electrons are returned to PSI, completing a cycle. This process generates ATP but does not produce NADPH or oxygen.

Purpose of Cyclic Photophosphorylation

To produce additional ATP required for the Calvin cycle when the energy demand exceeds the supply of ATP generated by non-cyclic photophosphorylation.

The Role of the Electron Transport Chain in ATP Generation

The electron transport chain (ETC)is crucial for ATP synthesis in both cyclic and non-cyclic photophosphorylation. Here’s how it works:

1.       Electron Transfer: High-energy electrons released from PSII (or PSI in cyclic photophosphorylation) move through a series of electron carriers embedded in the thylakoid membrane. As electrons flow through the chain, their energy is used to pump protons (H⁺) from the stroma into the thylakoid lumen.

2.       Proton Gradient and Chemiosmosis: The movement of protons into the thylakoid lumen creates a proton gradient, with a higher concentration of H⁺ inside the lumen compared to the stroma. This proton gradient represents stored potential energy.

3.       ATP Synthase and ATP Production: Protons flow back into the stroma through ATP synthase, driven by the gradient. The flow of protons provides the energy needed for ATP synthase to convert ADP and inorganic phosphate (Pi) into ATP. This process is called chemiosmosis.

Summary of ATP and NADPH Production

ATP: Produced in both cyclic and non-cyclic photophosphorylation by chemiosmosis.

NADPH: Produced only in non-cyclic photophosphorylation when electrons from PSI reduce NADP⁺.

Oxygen: Evolved in non-cyclic photophosphorylation as a byproduct of water photolysis.

Light-Independent Reaction (Calvin Cycle)

The light-independent reactions, also known as the Calvin cycle or Calvin-Benson cycle, occur in the stroma of the chloroplast. This cycle does not directly use light energy but relies on the ATP and NADPH generated during the light-dependent reactions to fix and reduce carbon dioxide, ultimately synthesizing carbohydrates.

Overview of the Calvin Cycle

The Calvin cycle consists of three main phases:

1.       Carbon Fixation

2.       Reduction

3.       Regeneration of Ribulose Bisphosphate (RuBP)

Carbon Fixation

·       Starting Molecule- The cycle begins with the 5-carbon compound ribulose bisphosphate (RuBP).

·       Enzyme Involved: The enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) catalyzes the first step.

·       Process:

1.       CO₂ Fixation: A molecule of carbon dioxide (CO₂) is fixed (combined) with RuBP.

2.       The resulting 6-carbon compound is highly unstable and immediately splits into two molecules of 3-phosphoglycerate (3PG), which is a 3-carbon compound.

·       Reaction Summary:  RuBP (5C) + CO₂ (1C) —>Two 3PG (3 C each)

Reduction Phase

The ATP and NADPH produced in the light-dependent reactions are utilized in this phase to convert 3PG into glyceraldehyde-3-phosphate (G3P), a 3-carbon sugar that can be used to form carbohydrates. Process:

1.       Phosphorylation of 3PG: Each molecule of 3PG receives a phosphate group from ATP, forming 1,3-bisphosphoglycerate (1,3-BPG). ATP is converted into ADP in the process.

2.       Reduction of 1,3-BPG: 1,3-BPG is reduced to glyceraldehyde-3-phosphate (G3P) using electrons from NADPH. NADPH is oxidized to NADP², and the phosphate group is released.

Reaction Summary: 3PG+ ATP 1,3-BPG  1,3-BPG+ NADPH G3P+NADP⁺ + Pi

Outcome: For every three molecules of CO₂ that enter the cycle, six molecules of G3P are produced. However, only one G3P molecule is used to synthesize carbohydrates, while the other five G3P molecules are used to regenerate RuBP.

Regeneration of RuBP

The regeneration phase ensures the cycle can continue. The five G3P molecules not used to form carbohydrates are rearranged to regenerate three molecules of RuBP. Process:

1.       Rearrangement and Phosphorylation: The five 3-carbon G3P molecules are converted into three 5-carbon RuBP molecules using ATP. This step involves a complex series of reactions where the carbon atoms are rearranged.

2.       ATP Consumption: ATP provides the necessary energy to convert G3P back into RuBP.

Reaction Summary: 5G3P (3C each) + 3ATP —>3RuBP (5C each)

The Use of ATP and NADPH in the Calvin Cycle

1.       ATP: ATP provides the energy needed for the phosphorylation steps, including the conversion of 3PG to 1,3-BPG and the regeneration of RuBP. In total, 9 ATP molecules are used per three CO₂ molecules fixed.

2.       NADPH: NADPH supplies the reducing power (electrons) needed to convert 1,3-BPG to G3P. 6 NADPH molecules are consumed per three CO₂ molecules fixed.

Synthesis of Carbohydrates

• Glyceraldehyde-3-Phosphate (G3P): The main product of the Calvin cycle is G3P, which serves as the starting material for the synthesis of glucose and other carbohydrates.

• Glucose Formation: Two G3P molecules combine to form one molecule of glucose (6-carbon sugar) through a series of reactions in the cytoplasm or the chloroplast.

Factors effecting the rate of photosynthesis

Photosynthesis is influenced by several environmental factors, including light intensity, wavelength of light, carbon dioxide concentration, and temperature.

Effects of Light Intensity on Photosynthesis

• Role of Light: Light provides the energy required for the light-dependent reactions of photosynthesis, which produce ATP and NADPH.

• Light Intensity and Rate: At low light intensities, the rate of photosynthesis is limited because there is insufficient energy to drive the light-dependent reactions. Consequently, the production of ATP and NADPH is reduced, slowing down the Calvin cycle. As light intensity increases, the rate of photosynthesis also increases because more energy is available to excite electrons in photosystems I and II. This leads to higher ATP and NADPH production, accelerating the Calvin cycle.

• Saturation Point: When light intensity reaches a certain level, the rate of photosynthesis plateaus. At this point, other factors (such as carbon dioxide concentration or temperature) become limiting. Beyond this point, further increases in light intensity have no effect on the rate of photosynthesis.

• Photoinhibition: Extremely high light intensities can damage the chlorophyll and photosynthetic apparatus, reducing the rate of photosynthesis.

Effect of Wavelength of Light on Photosynthesis

• Photosynthetic Pigments: Chlorophyll absorbs light most efficiently in the red (approximately 660–700 nm) and blue (approximately 430–450 nm) regions of the electromagnetic spectrum. It absorbs green light less effectively, which is why plants appear green.

• Wavelength Impact:

  • Blue and Red Light: These wavelengths are optimal for photosynthesis. The rate is highest when the plant is exposed to blue and red light because chlorophyll pigments absorb these wavelengths well.

  • Green Light: Chlorophyll reflects green light, and photosynthesis occurs at a much lower rate under green light compared to red or blue light.

Effect of Carbon Dioxide Concentration on Photosynthesis

• CO₂ Concentration and Rate: At low carbon dioxide concentrations, the rate of photosynthesis is limited because there is not enough substrate for the Calvin cycle to proceed efficiently. As CO₂ concentration increases, the rate of photosynthesis also increases because more CO₂ is available for fixation, leading to a higher production of G3P and other organic molecules.

• Saturation Point: Once the CO₂ concentration reaches a certain level, the rate of photosynthesis plateaus. This is because RuBisCO and other enzymes involved in the Calvin cycle become saturated, and further increases in CO₂ concentration do not enhance the rate.

Effects of Temperature on Photosynthesis

• Enzyme Activity: Photosynthesis involves several enzyme-catalyzed reactions, particularly in the Calvin cycle. Enzymes are sensitive to temperature changes.

• Temperature and Rate: At low temperatures, enzyme activity is reduced, and the rate of photosynthesis is slow. The kinetic energy of molecules is low, which decreases the frequency of collisions between enzymes and substrates. As the temperature rises, the rate of photosynthesis increases because enzyme activity is enhanced, and the reactions occur more rapidly.

• Optimum Temperature: There is an optimum temperature range (usually between 25°C and 35°C for most plants) at which the rate of photosynthesis is highest.

• High Temperatures: Beyond the optimum temperature, the rate of photosynthesis declines. High temperatures can denature enzymes, disrupt membrane structures, and cause increased water loss through transpiration. These factors decrease the efficiency of photosynthesis.

Limiting Factor

states that the rate of a physiological process (like photosynthesis) is determined by the factor that is in the shortest supply. Even if all other conditions are optimal, the process cannot proceed faster than the slowest, rate-limiting factor.

Interaction of Limiting Factors

At any given time, the rate of photosynthesis is determined by the factor that is most limiting. As one factor becomes sufficient, another factor may become the limiting one

Compensation Point

The compensation point is the light intensity (or CO₂ concentration) at which the rate of photosynthesis equals the rate of respiration. At this point, the net exchange of gases between the plant and the environment is zero.

Compensation Point Explanation

Below the Compensation Point: The rate of respiration exceeds the rate of photosynthesis. The plant consumes more oxygen and releases more carbon dioxide than it produces. Above the Compensation Point: The rate of photosynthesis exceeds the rate of respiration. The plant produces more oxygen and absorbs more carbon dioxide than it consumes.

C3 Plants and the C3 Pathway

• Definition: C3 plants use the Calvin cycle for carbon fixation, where the enzyme RuBisCO fixes CO₂ to a 5-carbon molecule, ribulose bisphosphate (RuBP), forming two molecules of 3-phosphoglycerate (3PG), a 3-carbon compound. This is why it is called the C3 pathway.

• RuBisCO: This enzyme has a dual function, acting as both a carboxylase (binding CO₂) and an oxygenase (binding O₂). The oxygenase activity leads to a wasteful process called photorespiration.

• Photorespiration: When RuBisCO binds oxygen instead of carbon dioxide, a 2-carbon molecule, phosphoglycolate, is produced. This compound cannot be used in the Calvin cycle and must be converted back to useful forms through a complex process that consumes ATP and releases CO₂.

• Conditions Promoting Photorespiration: High temperatures and low CO₂ concentrations increase RuBisCO's oxygenase activity, reducing the efficiency of photosynthesis.

C4 plants adnd C4 pathway

• Definition: C4 plants have developed a mechanism to minimize photorespiration and enhance carbon fixation efficiency under high light intensity, high temperatures, and low CO₂ conditions.

• C4 Carbon Fixation: CO₂ is first fixed in the mesophyll cells using the enzyme phosphoenolpyruvate (PEP) carboxylase, which has a higher affinity for CO₂ and does not react with O₂. This reaction produces a 4-carbon compound, oxaloacetate, which is quickly converted to malate or aspartate. The 4-carbon compound is then transported to the bundle sheath cells, where CO₂ is released and refixed by RuBisCO in the Calvin cycle. This spatial separation of initial CO₂ fixation and the Calvin cycle helps to concentrate CO₂ around RuBisCO, reducing the chances of photorespiration.

• Ecological Adaptation: The C4 pathway allows plants to photosynthesize efficiently in hot, dry environments by minimizing water loss and reducing photorespiration.

CAM plants (Crassulacean Acid Metabolism)

• Definition: CAM plants have adapted to extremely arid environments. They use a modified form of carbon fixation that separates processes by time rather than space.

• Mechanism: Night: Stomata open, and CO₂ is fixed using PEP carboxylase to form organic acids (mainly malic acid), which are stored in vacuoles. Day: Stomata close to conserve water. The stored organic acids release CO₂, which enters the Calvin cycle.

• Ecological Adaptation: CAM plants conserve water by opening their stomata at night, reducing water loss in hot, dry climates.

Comparison of C3 and C4 pathways as Ecological Adaptations

• C3 Plants: Environment: Thrive in cooler, moist climates where photorespiration is less of a concern. Limitation: In hot and dry conditions, photorespiration significantly reduces the efficiency of photosynthesis. Water Use Efficiency: Lower water use efficiency due to the need to keep stomata open longer for CO₂ uptake.

• C4 Plants: Environment: Adapted to high temperatures, intense sunlight, and low CO₂ concentrations. Advantage: By concentrating CO₂ around RuBisCO in bundle sheath cells, photorespiration is minimized, and water use efficiency is improved. Water Use Efficiency: Higher water use efficiency because they can close their stomata more frequently, conserving water.

• CAM Plants: Environment: Adapted to extremely arid conditions where water conservation is crucial. Mechanism: Temporal separation of carbon fixation and the Calvin cycle allows CAM plants to photosynthesize with minimal water loss. Water Use Efficiency: Extremely high water use efficiency due to nocturnal CO₂ uptake.

C3 leaf structure

• Mesophyll Cells: Uniformly distributed throughout the leaf, with chloroplasts present in each cell.

• Bundle Sheath Cells: Not well developed or specialized for photosynthesis. The Calvin cycle occurs only in the mesophyll cells.

• Chloroplast Distribution: All chloroplasts are similar and participate in the Calvin cycle.

C4 leaf structure

• Kranz Anatomy: Characteristic of C4 plants, referring to the arrangement of cells in a wreath-like (Kranz) pattern around the vascular bundles.

• Mesophyll Cells: Surround the bundle sheath cells and are involved in the initial fixation of CO₂ using PEP carboxylase.

• Bundle Sheath Cells- Form a tight layer around the vascular bundles and contain large, specialized chloroplasts where the Calvin cycle occurs. These chloroplasts are isolated from oxygen to minimize photorespiration.

• Two Types of Chloroplasts:

  • Mesophyll Chloroplasts: Contain enzymes for the initial fixation of CO₂ and are less equipped for the Calvin cycle.

  • Bundle Sheath Chloroplasts: Lack grana (or have reduced grana) and are specialized for the Calvin cycle. These chloroplasts accumulate CO₂ to saturate RuBisCO and suppress photorespiration.

Nutrition

The process of acquiring energy and materials for cell metabolism, including the maintenance and repair of cells

Heterotrophic nutrition

Heterotrophic organisms cannot synthesise their own food, and therefore depend on autotrophs to meet their nutritional requirements. Heterotrophs generally feed on other organisms to obtain chemical energy by degrading their organic molecules.

Holozoic nutrition

It is observed mainly in the majority free-living organisms with a specialised digestive tract. Holozoic feeders take food into their bodies and then digest it. Organisms that show this nutrition include:

• Predators

• Detrivores

• Filter feeders

• Fluid feeders

• Absorptive feeders

• Substrate feeders

Predators

Animals that feed on living organisms

Herbivores

Prey on plants

Carnivores

Pray on animals

Omnivores

Prey on both

Detrivores

organism that feed on detritus i.e. small pieces of dead and decomposing plants and animals. Example woodlice

Filter feeders

prey on small organisms by filtering them from the aquatic environment. Example flamingo

Fluid feeders

such as aphids obtain food from the fluids produced by various organisms, including blood and nectar

Absorptive feeders

such as tapeworms, live in a digestive system of another animal and absorb nutrients from that animal directly through their body wall. Parasites- feed on other living organisms

Substrate feeders

such as earthworms and termites, eat the material (dirt or wood) they burrow through.

Saprophytic nutrition

Mostly protoctists and fungi, absorbs nutrients from dead organic matter.

Symbiotic nutrition

Is observed when two or more organisms of different species live together in close association. Three common types of symbiotic relationships are: Mutualism, Parasitism, Commensalism

Mutualism

In which both partners benefit

Parasitism

In which one partner benefits and causes harm to the other

Commensalism

In which one partner benefits but the other receives no harm or benefits

Metabolic rate

The measure of the overall energy needs that must be met by the animal’s food.

Basal Metabolic Rate (BMR)

The metabolic rate resulting from all of the essential physiological function that take place in a resting, fasting state. It is the minimum rate of energy requirement at rest. This is determined by:

• Age- children have a higher BMP than adults as they are still in their growing phase

• Sex- males have a slightly higher BMR than Females

• Body size- the smaller the organism the higher the BMR to make up for increased heat losses due to a higher SA:V

• Hormones- level of thyroxine affects the BMR

Ingestion

Introducing large pieces of food into the alimentary canal

Digestion

Breaking down the food by mechanical and chemical methods. Chemical digestion involves the breakdown of large biomolecules into smaller ones. Reactions are catalysed by specific reactions

Absorption

The useful soluble digestion products are transported across the cells lining the gut wall into the bloodstream and lymph

Assimilation

The absorbed molecules are transported in the bloodstream to the body cells. They are stored, broken down by respiration to generate energy or used by cells to maintain good health for growth or to repair body tissues

Egestion

Elimination of the undigested material from the alimentary canal through the anus

Sac-like plans

Found in many invertebrates, which have a single opening for food intake and the discharge of wastes. Example the gastrovascular cavity in cnidarians

Tube within a tube plan

Where food enters through one opening (the mouth) and wastes leave through another (the anus). Example alimentary canal in vertebrates

Intracellular digestion

Food particles are taken into cells by phagocytosis. these food vacuoles fuse with lysosomes containing digestive enzymes, bringing about digestion. Intracellular digestion occurs commonly in heterotrophic protoctists (protozoans) and in sponges.  

Extracellular digestion

Digestion that occurs outside cells. Cells release hydrolytic enzymes into the lumen (hollow) of the digestive system, with the nutrient molecules being transferred to the blood or body fluid. Extra cellular digestion is observed in chordates, annelids, and arthropods.

The structure of the alimentary canal

Digestion and absorption of food occur in the alimentary canal. This is a long (6-9 meters long when fully extended), coiled, hollow, muscular tube. It is divided into several regions, each region being specialised to carry out particular steps in the overall process of mechanical and chemical digestion and absorption of food. Movement of food occurs only in one direction, namely from the mouth to the anus.

mouth

mechanical and chemical processing, chewing reduces the size of food; saliva digest carbohydrates

oesophagus

Transport food by peristalsis

Stomach

Mechanical and chemical processing; digestion of proteins

Small intestine

Chemical processing and absorption, digestion of proteins, fats, carbohydrates; absorption of nutrients and water  

Large intestine

Water absorption and feces formation

rectum

Holds feces

Anus

Feces elimination

Salivary glands

Secrete enzymes that digest carbohydrates; supply lubricating mucus

Liver

Secretes molecules required for digestion of fats

Gallbladder

Stores secretions from liver; empties into small intestine

Pancreas

secretes enzymes and other materials into small intestine